Either congenitally or by acquisition, abnormal openings or holes can occur between adjacent chambers of the heart or its associated major blood vessels. Such openings are referred to, respectively, as interatrial and interventricular septal defects or patent ductus arteriosus and aortico-pulmonary windows. Such openings cause blood to leak from one chamber or artery to another and result in decreased pumping efficiency of the heart. Similarly, if defects occur in the Foramen Ovale, such defects, referred to as Patent Foramen Ovale (PFO), may result in a cerebral embolism. These deformities usually are congenital, however, they can also occur following a heart attack, significantly complicating subsequent coronary treatment and recovery. Such defects typically impose added strain on the heart and ultimately may lead to heart failure if not corrected.
Traditionally, such defects have required extensive open chest surgical techniques for correction. Specifically, the repair of such defects required an open heart procedure in which the heart was exposed and then opened and the defect was sewn shut by direct suturing. In connection therewith, a patch of a synthetic prosthetic material such as Dacron, Teflon, silk, nylon or pericardium was used to repair the defect.
Although other methods of occluding defects, most notably the use of a plastic plug to occlude the defect, were suggested as early as the 1950s, such methods similarly require the use of open heart surgery to access the defect and place the prosthetic implant.
Beginning in the early 1970s, a number of devices and methods were proposed for the percutaneous transluminal catheterization procedure for the repair of intracardiac defects. For example, U.S. Pat. No. 3,874,388 to King, et al., describes a device in which a pair of umbrella-like occluders are positioned on opposite sides of a defect and drawn and locked together at a central hub which crosses the defect. The device is said to effectively occlude the defect. Although the King device and method proposed to eliminate the need to perform open heart surgery, its use and structure were very complicated in that generally they required the umbrella-like occluders to be opened manually once positioned at the defect.
Similarly, U.S. Pat. No. 4,007,743 to Blake relates to an umbrella-like defect closure device having a plurality of elongated struts pivotally mounted to a central hub. Each pair of adjacent struts is interconnected by a strip formed of a foldable, resilient material which serves to automatically and resiliently open each umbrella-like element once such element is released from a protective sheath. As in the King patent, the device includes two separate occluders which are locked together by a snap connection once each of the occluder segments has been individually positioned across the septal defect.
Still another defect closure device is described in U.S. Pat. No. 4,917,089 to Sideris. The Sideris patent relates to an apparatus and method for transvenous closure of a septal perforation in the heart. The closure apparatus comprises an occluder which is positioned on the distal side of the perforation and an occluder-holder which is positioned on the proximal side of the perforation and is connected to the occluder across the perforation by means of a so-called "button" closure. As in the earlier transluminally delivered occluders, the Sideris patent requires that device elements positioned on opposite sides of a septal defect are separately delivered to the site of the defect and connected to one another in situ.
In U.S. Patent application Ser. No. 08/227,585, which is a continuation of Ser. No. 07/787,940, now abandoned, which corresponds to published European Application No. 0545091A2 entitled "Occluder and Method for Repair of Cardiac and Vascular Defects" attempts to overcome problems associated with the aforementioned devices are described. The application describes a device having separate occlusion elements that are connected in a manner such that they may be oriented in aligned or nonaligned relationships across the defect. Such a device is particularly useful in the repair of tunnel-like defects or defects having a non-uniform wall thickness. The application also describes a device having occlusion elements that are fluoroscopically distinguishable from one another, thereby enhancing the ability of a physician to visualize the device fluoroscopically during a percutaneous, transluminal placement procedure.
The devices of the application described above typically comprise a series of elongated struts attached at a central point and having two flexural pivot points thereon. For example, in one embodiment, each elongated strut includes a first coil located on the strut at a position adjacent to a central portion of the device, (referred to as a "shoulder" hinge), and a second coil located on the strut at a position remote from the shoulder, (referred to as an "elbow" hinge). Despite the numerous advantages associated with the occluders described in the application above, on occasion such devices may fail as a result of stress or fatigue after a limited time in vivo. In particular, failures have occurred on the strut arm at the elbow hinge or at a region immediately adjacent thereto. Although such failures have resulted in no clinical problems, (since the occluder rapidly becomes encapsulated in tissue prior to the incidence of failure), it would be desirable to eliminate even the possibility of such failures as a means of eliminating a potential source of complications.
Accordingly, a need exists for a device for the occlusion of cardiac and vascular defects that can withstand the full range of stresses applied to the device over a prolonged period of time in an in vivo environment. In connection therewith, a need exists for a vascular occluder configured in a manner such that flexural stresses are minimized and distributed throughout the device in order to provide an occlusion device that will not undergo stress failures in vivo.